1. Field of the Invention
The present invention relates to a process for preparing a filter, and more particularly to a process for preparing a filter suitably applicable to a color display in liquid crystal display devices, etc.
2. Related Background Art
Color filters are of many types, among which such a type is well known as that based on a colored resin film composed of a mixture of a photosensitive resin and a coloring material because of its relatively good heat resistance and simple process steps.
Generally, a color filter has been so far formed on a substrate by patterning according to a photolithographic process, where the patterning is carried out by applying a colored resin to a substrate by an ordinary coating procedure such as spinner method, printing method, roll coater method, etc., then prebaking the applied resin on a hot plate or in an oven, exposing the prebaked resin to light through a photomask, dipping the resin into a developing solution, thereby conducting development, followed by postbaking with heating again at a higher temperature than the prebaking temperature to form a pattern for a color filter.
A substrate for a liquid crystal display device has been so far prepared by forming a transparent insulating film on the thus formed color filter mainly to make surface flattening, then forming a transparent electrode, and further a metallic electrode, etc. thereon successively, followed by patterning to obtain a substrate provided with a color filter having a plurality of stripe-form electrodes.
As the transparent insulating film, inorganic films of SiO.sub.2, TaO.sub.x, etc., transparent resin films, photosensitive transparent resin films, etc. have been so far used, and with patterning in some cases.
However, in the above-mentioned conventional process, particularly when the colored resin applied to the substrate is exposed to light and developed in the developing solution by photolithographic process, the chemical dissolution rate of non-exposed parts is low, and in some cases a coupling agent is contained in the colored resin to improve the adhesiveness between the colored resin on the light-cured parts and the substrate. Particularly near the interface of the substrate, the colored resin of non-exposed parts cannot be completely removed, even if the dipping time in the developing solution is prolonged until the surfaces of light-cure parts are toughened, and sometimes the colored resin remains as residues on the interface of the substrate.
The residues can be removed to some extent by washing with a solvent, etc. but it is very difficult to completely remove the residues. That is, the residues often remain as a very thin layer on the substrate surface. In the successive step of forming another color film or forming a transparent electrode or a metallic electrode as a film, followed by patterning, the residues deteriorate the adhesiveness between these films and the substrate and thus serve as a cause for peeling of these films. Particularly at the mounting part where a liquid crystal panel of a liquid crystal display device is connected to a driver for driving the device, a physically large force is easily applicable to the mounted electrode on the substrate to readily peel the mounted electrode from the substrate. A result occasion of such peeling lowers the yield or durability of liquid crystal display devices as important disadvantages.